Urea has been long recognized as a cosmetic ingredient in formulations acting as a humectant and moisturizer. High concentrations of urea, such as 40%, are also known to have mild, antibacterial effect. At these strengths the antibacterial effects are said to be similar to those of antibiotics, with the further advantage that all the common organisms are susceptible and the possibility of resistant strains need not be seriously considered. There have been reports of keratolytic activity attributed to urea with the ability at high concentrations to solubilize and denature protein. Concentrated solutions of urea can change the conformation of protein molecules. A striking effect is upon the water-binding capacity of the horny layer of the skin: pieces of normal horny layer, or scales from ichthyotic or psoriatic skin that have been soaked in 30% urea solution take up much more water. This is important because in maintaining the flexibility of the horny layer and the softness of the skin, the water content of the horny layer matters much more than its oil content.
Fungal infections of the nail are notoriously difficult to treat. Traditional, topical therapies cannot penetrate the nail plate, and eradicate the infection in and under the nail bed; they are useful only in milder forms of the disease. Systemic antifungal drug therapy is associated with potentially harmful side effects. Since oral antifungals are distributed throughout the entire body, systemic side effects such as elevated liver enzymes, gastrointestinal disorders and skin rashes are not uncommon and may require expensive medical intervention and laboratory tests.